The present invention relates to a method of bonding at least two types of refractory ceramic materials comprised within the Al.sub.2 O.sub.3 /SiO.sub.2 system, especially fireclay and alumina, to each other, and particularly to enhance both the abrasion and corrosion resistances of refractory or heat resistant plates for valve closures of foundry stopper ladles.
As known, steel is cast at present from foundry ladles provided with stopper rods having stopper plugs. However, such a simple arrangement has many disadvantages: the stopper rod consisting of a plurality of stopper rod parts has to be exchanged for a new one after each heat, a relative high consumption of stopper pipes prevents high-grade materials from being used for the manufacture thereof while currently applied materials such as fireclay or fireclay-graphite compositions do not offer the full reliability expected from the stopper or plug mechanisms, the plug and the stopper pipes become worn out by superficial melting, and the stopper may eventually become burned off, all of which make the casting process defective. Among other disadvantages, there can also be named laborious preliminary steps before the casting process since the ladle has to be pre-cooled which in turn endangers effective life of the oven lining, or which makes it necessary to use a protective caisson making the maintenance work troublesome. Foundry ladles equipped with plug or stopper mechanisms may not be heated to highly elevated temperatures since possible dents or cracks arising as a result in the ceramic material of which the stopper rod is made from may cause failures in the casting process.
Developments in modern technological steel making proceses such as vacuum degassing and continuous casting make it necessary to provide new foundry ladle sealing modes. In endeavors to eliminate the disadvantages of plug closures of foundry ladles, there has been developed a valve closure the plates of which are made of refractory ceramic materials based on corundum, zirconium silicate, or, alternatively, magnesite. However, such technology is rather demanding since it requires additional plants as well as high firing temperatures exceeding 1600.degree. C.
During a single casting cycle, multiple shifts of a movable plate of the valve on a stationary plate thereof occur. As a result, the surfaces of said valve plates are abraded and roughened, which may eventually impair the tightness of the valve closure. Apart from this, the outflow hole in the valve plates becomes worn out, due to the erosive action of molten steel, which can result in an uncontrollable enlargement of said hole and, consequently, in an undesirable change in the rate of casting.
To mitigate the above disadvantages it has been proposed to provide the basic material, which has a lower initial deformation temperature, with an upper or coating layer of another material having a higher initial deformation temperature as well as both higher abrasion and corrosion resistances. Such a solution of the problem, however, is rather questionable since it is hardly possible sufficiently to bond the two materials to each other. Thus, although the coating material exhibits better characteristics than the basic one, these characteristics remain essentially unutilized due to an imperfect bond between the two materials, so that the advantages achieved have been rather poor.
It is an object of the present invention to remove the above referred to drawbacks of the prior art, and to attain a substantially better effect in bonding the basic and the coating material to each other, to utilize, to their full extents, the abrasion and corrosion resistences to the latter, and thus to enhance the reliability and life of the bonded material relative to prior art.